1. Field of the Invention
The present invention relates to a timer-assisted photographing mode control device for a camera suitable for use in automatic intermittent and unmanned photography.
2. Description of Related Art
A typical known timer-assisted device for controlling the photographing mode of a camera will be described with reference to FIG. 1.
The device has a timer circuit 1 which is capable of producing a predetermined output at its output terminal b upon receipt of a signal of a high (H) level at its input terminal a. The device also has a D flip-flop 2 having an input terminal D and a clock terminal CLK. In response to each rise of the signal level at the clock terminal CLK, the flip-flop 2 latches the input signal which is input to the input terminal D and delivers the latched value through an output terminal Q while delivering an inverse output through another output terminal Q thereof. The clock terminal CLK is grounded through a resistor 4 and is connected through a timer operation switch 3 to a power supply (not shown) which provides a source voltage of the H level. The output terminal Q is connected to the input terminal a of the timer circuit 1. A reference numeral 5 denotes a camera control circuit. When the level of the signal supplied to a first input terminal SW1 is reduced to a low (L) level, the camera control circuit 5 activates a camera control system so as to commence operation, such as photometry. When a signal of the H level is received by a second input terminal SW2, the camera control system conducts a shutter releasing operation. In addition, the camera control circuit 5 provides a trigger output terminal TRIG which delivers a pulse of the H level and has a constant duration in response to each shutter releasing operation. The trigger output terminal TRIG is connected to the input terminal c of the timer circuit 1. The timer circuit 1 counts the number of the pulses from the trigger output terminal TRIG and maintains an output of the H level at its output terminal b until the number of the pulses reaches a predetermined set value. A reference numeral 15 denotes a range-finding circuit of the camera. This circuit conducts a range-finding operation when a signal of a low (L) level is received by the input terminal SW1' thereof and, when an in-focus state is obtained, produces an output of the H level at its output terminal AFOK. The input terminal SW1' is grounded together with the first input terminal SW1 of the control circuit 5 through a first switch 10, while the output terminal AFOK is connected both to an AF output terminal AF of the control circuit 5 and one of the input terminals of a NOR circuit 13. The other input terminal of the NOR circuit 13 is connected to an AF mode switch 7 through an inverter 14. The output of the NOR circuit 13 is connected to one of the input terminals of an AND circuit having an inverter 12 (hereinafter referred to as an AND circuit 12) the other input terminal of which is connected both to a second switch 11 and a transistor 6. When the output terminal Q of the flip-flop 2 is set low, the timer circuit 1 does not operate so that the output terminal b of the timer circuit remains at the L level so as to keep the transistor 6 off. When the AF mode switch 7 is in an off state, the inverter 14 receives a signal of the H level so that it produces an output of the L level. Then, as the user presses a shutter release button of the camera, the first switch 10 is turned on so that the camera control circuit 5 and the range-finding circuit 15 start to operate.
As the shutter release button is further pressed, the second switch also is turned on. If the result of the range-finding operation shows that the camera is not in in-focus state, the range-finding circuit 15 delivers a signal of the L level at its output terminal AFOK so that the NOR circuit 13 receives inputs of the L level and, therefore, delivers an output of the H level. In consequence, the AND circuit continues to output a signal of the L level so that the camera does not begin the shutter releasing operation. Conversely, when an in-focus state is confirmed, the range-finding circuit 15 delivers an output of the H level at the output terminal AFOK thereof so that the output of the NOR circuit 13 is set to the L level. In consequence, the AND circuit 12 receives signals of the L level at its both input terminals so that it delivers an output of the H level, whereby the control circuit 5 conducts a shutter releasing operation.
On the other hand, if the AF mode switch 7 has been turned on, the inverter 14 delivers an output of the H level so that the output of the NOR circuit 13 is set to the L level regardless of the level of the signal from the output terminal AFOK of the range-finding circuit. Therefore, when the second switch 11 is turned on, signals of the L level are input to both input terminals of the AND circuit 12, thereby to commence the shutter releasing operation. It will be seen that the AF mode switch 7 has a function for changing the mode of AF operation of the camera. Namely, when this switch 7 is in an off state, the camera operates in a first AF mode in which the shutter is not released unless an in-focus state is confirmed, whereas, when this switch is in on the state, the camera operates in a second AF mode in which the shutter is released in response to pressing of the second switch 11 regardless of the focusing state. The first AF mode inhibits the exposure unless the object is correctly focused and locks the optical system once the in-focus state is obtained. This mode, therefore, is suitable for use in the cases where the distance between the camera and the object is unchanged or where the framing operation is executed while a main object is brought into focus. In particular, the second AF mode is effective in shooting a moving object because the optical system automatically focuses the object regardless of the movement. Thus, the user can selectively use these two AF modes in accordance with the type of the object to be photographed.
This known photographing mode control device suffers from the following problem. It is assumed here that the timer operation switch 3 is instantaneously turned on to start the timer while the AF mode switch 7 is in an off state. In such a case, if the output from the output terminal AFOK of the range-finding circuit 15 remains at the L level, i.e., if the camera is in an out-of-focus state, the shutter is not released even when the predetermined output is delivered from the output terminal b of the timer circuit 1, and the shutter is released only after the output from the output terminal AFOK of the range-finding circuit 15 is turned to the H level, i.e., only after the in-focus state is established. This seriously impairs the function of the timer, i.e., exposure for a preset shutter opening time. In consequence, the photographing operation may fail due to inadequate exposure.
FIG. 2 shows another known timer-assisted photographing mode control device.
This device has a timer circuit 1001 having an input terminal a and an output terminal b, a D flip-flop circuit 1002 having a clock terminal CLK which is grounded through a resistor 1004, a timer operation switch 1003, a camera control circuit 1005 and a transistor 1006. As the release button of the camera is pressed, a first switch 1009 is turned on so as to set a first input terminal AW1 of the control circuit 1005 to the L level thereby to start a camera system, thus commencing a photometry operation, a range-finding operation and other operations. As the release button is further depressed, a second switch 1008 is turned on so as to set a second input terminal SW2 of the control circuit 1005 at the L level, thereby executing a releasing operation. The control circuit 1005 also controls the operation of a film winding motor such as to enable the camera to operate selectively in a single-shot mode in which only one frame of film is exposed and a continuous-shooting mode in which consecutive frames are exposed. More specifically, when the S/C switch 1007 is turned on to set a third input terminal S/C to the L level, the control circuit 1005 selects the continuous shooting mode in which a shutter releasing operation and preparation for releasing, e.g., film feeding and shutter charging, are executed alternately as long as the second input terminal SW2 is set at the L level. Conversely, when the S/C mode switch 1007 is in off state, the third terminal S/C is not at the L level. In this case, the releasing operation is executed when the second input terminal SW2 is set to the L level followed by preparation for releasing. In this case, however, the next releasing operation is inhibited until both the first input terminal SW1 and the second input terminal SW2 are set to the L level. The state of the S/C mode switch 1007 is changeable manually by the photographer depending on whether the photographer wishes to conduct continuous photographing or wishes to avoid unintentional continuous photographing. Namely, when the continuous photographing is not necessary, the photographer operates the S/C mode switch 1007 such that the L level does not appear at the third input terminal S/C. In consequence, the camera operates in a single-shot mode. To take the next photograph, the photographer frees the release button to temporarily turn off the first and second switches 1009 and 1008 and then turns on these switches again.
On the other hand, when a signal of the H level is input to the input terminal a of the timer circuit 1001, the timer circuit 1001 delivers from its output terminal b a release signal composed of one, two, or more, pulses at a predetermined time interval. The release signal serves to turn the transistor 1006 on so as to set the second input terminal SW2 of the control circuit 1005 to the L level, thereby starting the shutter releasing operation. The input terminal a of the timer circuit 1001 is connected to the output terminal Q of a D flip-flop 1002. When the timer operation switch 1003 is turned on, a signal of the H level from a power supply (not shown) is delivered to the clock terminal CLK of the D flip-flop 1002. The flip-flop 1002 latches the input available at the input terminal D each time the level of the signal at the clock terminal CLK rises and delivers the latched value through its output terminal Q while returning the inverted output Q to the input terminal D.
Therefore, when the timer operation switch 1003 is turned on instantaneously, the Q output of the D flip-flop 1002 is inverted to the H level, so that the timer circuit 1001 produces a signal of the H level at its output terminal b at the predetermined time interval. In consequence, the transistor 1006 is turned on so that the second input terminal SW2 of the control circuit 1005 is set to the L level, whereby the camera conducts intermittent photography at the predetermined time interval. When the switch 1003 is turned on again, the timer circuit 1001 stops operating so that the intermittent photographing operation ceases.
The following problem is encountered with the photographing mode control device of FIG. 2.
Usually, the timer-assisted photography is conducted in an unmanned condition. Namely, the photographer leaves the camera after setting the camera in a timer-assisted photographing mode. In this photographing mode control device, the selection of operation mode is possible only through the manipulation of the S/C mode switch 1007. Namely, the photographer has to turn the S/C mode switch on before he leaves the camera, when he wishes to take a plurality of photographs at a predetermined time interval. Unfortunately, however, it often happens that the photographer forgets to turn the S/C mode switch 1007 on and becomes aware of this fact only after the set time has expired.
A proposal has been made for the purpose of eliminating this disadvantage. According to this proposal, if the camera is set for intermittently taking photographs at a time interval T.sub.1 such that two frames are exposed each time as shown in FIG. 3(a) while the third input terminal S/C has not been set to the L level, an on signal (the L level) and an off signal (the H level) are delivered to the first and second input terminals SW1 and SW2 of the control circuit 1005 from the timer circuit 1001, as shown in FIG. 3(b). This, however, requires a complicated control means which is capable of performing, before and after each time interval, a series of controlling operations including turning on of the first and second input terminals SW1 and SW2, detecting completion of the shutter releasing operation, keeping the first and second input terminals SW1 and SW2 in an off state for a predetermined period, turning on again the first and second input terminals SW1 and SW2, detecting completion of the shutter releasing operation, and turning the first and second switches SW1 and SW2. This complicated process undesirably prolongs the period T.sub.2 between two shots in each shooting cycle.
If the levels of the signals at the first and second input terminals SW1 and SW2 are controlled as shown in FIG.3(c) while the third input terminal S/C has not been set at the L level, the camera only makes one photograph in each shooting cycle at the time interval T.sub.1 , thus failing to meet the photographer's expectations.